It is known that the use of a collimated backlight and a front diffusing screen can greatly improve the quality of an LCD. One such approach is described in Saccomanno (U.S. Pat. No. 6,428,198), which is incorporated herein by reference. Saccomanno describes the use of an arc lamp, whose light is collected, homogenized, and coupled into an array of optical conduits. Each conduit then illuminates a non-imaging optic, which collimates the light and subsequently illuminates the edge of a light-extraction guide.
Even though my prior patent teaches an effective collimated light and diffuser screen arrangement, for certain applications such as medical imaging there is a need to improve black-level contrast and image sharpness even at the expense of a slightly larger and less light efficient device.